Polycarbonate molding compositions containing an aromatic carbonate polymer and an ester have been disclosed in GB 1,567,517. Accordingly, esters of certain organic acids and certain alcohols can be incorporated in a thermoplastic aromatic polycarbonate resulting in a resin having release properties. In addition, the composition is said to be compatible with polycarbonate melt. The incorporation of the esters in the polycarbonate composition in accordance with the '517 document can be effected by admixing the ester with granules of polycarbonate composition and subsequently extruding these through an extruder under standard conditions. The esters may also be incorporated by dissolving them in a solvent in which the polycarbonate is dissolved and subsequently recovering the polymer composition from the solvent by known methods.
The preparation of relevant copolycarbonates was disclosed by Schreckenberg in U.S. Pat. No. 4,281,101. The process involved solution reaction of oligomers with diphenols. In accordance with the process disclosed in the '101 document, an aliphatic aromatic polycarbonate with diphenol carbonate end groups is prepared by reacting in the melt an aliphatic diol,carbonic acid bis aryl ester--for example diphenyl carbonate--and diphenols. The resulting polycarbonate is characterized in that each of its end groups constitute a residue of one diphenol. The polycarbonate disclosed in the '101 document are unsuitable in the practice of the present invention for the preparation of block copolycarbonates. It was surprisingly found that in instances where each of the end groups constitute residues of less than 2 diphenol units, the oligocarbonate was unsuitable for the preparation of copolycarbonates by melt blending with a polycarbonate resin. The product made with such unsuitable oligocarbonate was typically delaminated.